The present invention relates to a method for preparing an analytical sample of the slag which generate in the refining process of metals and to an apparatus for preparing the same. In particular, the present invention relates to a method for preparing a slag sample from slags that are generated in the refining process of steel, which is subjected to an on-line rapid analysis using fluorescent X-ray spectroscopy, and to a sampler for use in the same.
In the case of refining a metal such as in the smelting process of steel, it is important to control the. composition of the slag so that a metal having the targeted composition can be obtained. Accordingly, it is preferred to properly control the refining process based on the results obtained by performing slag analysis during the smelting process. Furthermore, in a process of effectively reusing the ash resulting from a combustion furnace for disposing wastes, it is also desired .to control the slag composition.
For the slag analysis, generally used method is glass bead fluorescent X-ray analysis, because this method enables the analysis of a plurality of elements simultaneously and at a high precision. More specifically, this method comprises preparing a homogeneous glass-like sample by crushing the slag and fusing the size-reduced slag using a flux, for instance, sodium borate, at an amount about 10 times as large as that of the slag, and then subjecting the sample to fluorescent X-ray analysis. This method is characterized in that it is less influenced by the coexisting elements and that, a high analytical precision is achievable; however, this method suffers disadvantages as such that the sample preparation requires operations such as crushing, weighing, and fusing, and that the total analytical procedure generally requires a time duration of 30 minutes or longer.
In the light of such circumstances, the briquette method is sometimes employed as a simplified analytical method. As compared with the glass bead method, the time necessary for carrying out this method can be shortened because the operations of weighing and fusing can be eliminated; still, however, the method still consumes for at least 25 to 30 minutes because the vessel for use in crushing requires pre-washing using the crushed sample. Furthermore, even if the aforementioned glass bead method or the briquette method should be assembled as an automated system, it is still difficult to shorten the analytical time to 20 minutes or shorter, and hence, at present, the analytical results obtained on the slag cannot be immediately reflected to the refining operation.
As a means for overcoming the problems above, in JP-A-Hei9-166589 (the term xe2x80x9cJP-Axe2x80x9d as referred herein signifies xe2x80x9can unexamined published Japanese patent applicationxe2x80x9d) is disclosed a method comprising directly subjecting the sampled slag to fluorescent X-ray analysis. This method comprises inserting a sampler having a large flat surface into the molten slag layer to thereby allow the slag to adhere on the flat surface, pulling up the sampler from the slag layer, stripping off the solidified slag, and subjecting the plane of the slag which was not brought into contact with the sampler to the fluorescent X-ray analysis.
However, in the method above, it is found that the contact plane of the slag with the sampler undergoes cooling at a different cooling rate as compared with that of the plane which was not brought into contact with the sampler. Thus, segregation in composition of the slag occurs within the non-contact plane, i.e., the plane that was cooled at a rate slower than that in the contact plane. Accordingly, in the aforementioned methods, the analytical plane, which was the last to be solidified, exhibits a greatly differed composition as compared with the average composition of the slag, and hence fails to give the accurate average slag composition. Furthermore, in a refining process of steel, for instance, it is not always possible to obtain a flat analytical plane, because the viscosity of the slag fluctuates depending on the type of the steel or on the operational stage. This also is an advantageous which leads to an inferior analytical precision.
On the other hand, in JP-A-Hei10-170411 is disclosed a technique comprising inserting a columnar sample 20 mm or longer in side and having at least one flat plane 10 mm or larger in diameter into a slag layer, rapidly pulling up the sampler, stripping off the solidified slag, and subjecting the plane there of in contact with the sampler to fluorescent X-ray analysis.
In a practical refining process, however, it is not possible to surely sample a vigorously fluctuating slag by using the sampler above having such small sides each about 20 mm in length. Accordingly, in a practical process, a sampler increased in size is used, for instance, a sampler at least 50 mm in length, 50 mm in width, and 500 mm in height, is employed. In this case, the sampler becomes as heavy as to weight 10 kg or more; that is, the sampling operation by hand is no longer a simple method. That is, the operatability and practical advantages in the operation site become greatly impaired.
In the light of the circumstances above, an object of the present invention is to overcome the problems of the conventional technology, and to provide a method of sample preparation for use in the smelting process of fused metal such as steel, which enables a rapid and accurate analysis of slag, and which is capable of providing on-line instructions during the refining operation based on the analyzed results. It is also an object of the present invention to provide a sampler which can be easily handled for use in the method.
According to the present invention, there is provided a method of preparing a slag sample for use in fluorescent X-ray analysis, which comprises immersing a metallic hollow polygonal column having smooth outer surface into a molten slag and immediately pulling it up, and then using the contact plane of the slag adhered on the outer surface of the hollow polygonal column as the analytical plane. In the method of preparing the slag sample for use in fluorescent X-ray analysis above, it is preferred to use a slag sampler for fluorescent X-ray analysis below as the hollow polygonal column.
More specifically, the present invention provides as the sampler for use in the fluorescent X-ray analysis, a hollow polygonal column comprising a smooth outer surface, provided that the member constituting the hollow polygonal column is a metal having a thickness of 3 mm or greater.
In the sampler for fluorescent X-ray analysis above, the outer surface of said hollow polygonal column is preferably coated with a releasing agent, and said hollow polygonal column is preferably a hollow tetragonal column.
FIG. 1 is a longitudinal cross section showing an example of a slag sampling apparatus according to the present invention.